The present invention relates to an aqueous pour-on formulation of water insoluble insect growth regulator (IGR), and a method of treating animals using this formulation.
Traditionally, animals have generally been treated for the control of parasites, by either dipping the whole animal in a bath containing a parasiticidally effective agent or by spraying the entire body surface of the animal with such an agent. More recently, it has been found that a number of parasiticidally effective substances may be applied by localised application (so-called xe2x80x9cpour-onxe2x80x9d application). Although the parasiticidally effective substance is supplied by localised application, the active agent migrates so as to protect the whole external surface of the animal. By xe2x80x9clocalised applicationxe2x80x9d it is meant that the active ingredient is only applied to a minor portion of the outer surface of the animal, generally as a line or spot on the animal""s back.
Prior Art Formulations
(a) Non Aqueous Pour-On Formulations
Various pour-on formulations are described in Australian patent nos. 560078, 563723, and 546672. In most pour-on formulations, and in all current water insoluble IGR pour-on formulations known to the inventors, the active agent is dissolved in a non-aqueous solvent system to produce a suitable pour-on formulation.
It has become apparent that non-aqueous pour-on formulations also possess a number of disadvantages. In particular, the formulation may pose handling problems caused by the flammability or toxicity of the solvents, and lead to high tissue residue levels in animals treated with the formulations.
Formulations based on water immiscible solvents would either run off wet animals or be washed off by rainfall which occurred after treatment.
On contact with water, the active rapidly precipitates out of non-aqueous formulations which are based on water miscible solvents. If this formulation is applied to a wet animal, or if the animal is exposed to rain before the treatment has dried on the animal, the active precipitates out of solution and is deposited along the back of the animal, the solvents also being washed away by the rain. This hinders or prevents the spread of the active ingredient around the entire animal. This phenomenon is particularly important to those areas on the underside of the animal. This reduces the effectiveness of solvent only based formulations under these conditions.
(b) Aqueous Dip Formulations
An aqueous dip formulation of IGR is also known.
However, such a dip formulation would not be suitable as a pour-on formulation in either the undiluted or diluted state for the following reasons.
Undiluted Dip Formulation
This would not be satisfactory because:
(i) In order to deliver the same amount of active per animal, the dose volume would be too small. That is, 2 mL would be applied to the majority of animals, which would be a major issue for accurate dosing by farmers. A very small dose volume would be too localised to allow spreading to all parts of the animal as described above.
(ii) Due to the high levels of surfactants in an undiluted dip formulation, the presence of water, particularly high rainfall, would tend to wash the active off the animal.
Diluted Dip Formulation
This situation would arise where the above-mentioned dip formulation is diluted to achieve what would be considered a satisfactory concentration of active. However, this would not be satisfactory for the following reasons:
(i) If the dip formulation were diluted in a backpack or drum, the active would almost immediately commence to settle out of the formulation due to dilution of the suspending agent. This would create under/over dosing as described above.
(ii) Because the sedimented active would no longer be associated with the spreading/wetting agents, it would essentially be deposited along the line of application and have no means to disperse.
With regard to the possibility of aqueous pour-on formulations, and based on non-aqueous pour-on formulations, it would be expected by those skilled in this art that aqueous pour-on formulations containing water insoluble IGRs would not be effective because of problems with spreading and physical stability as follows.
Spreading
It has generally been believed that a non-aqueous solvent is required to both dissolve the water insoluble IGR and help disperse the active so that it reaches all parasites on the animal. Without such spreading, the active would not reach all of the parasites, and would therefore be ineffective. Such spreading, in particular with sheep, also involves the movement of the active into the greasy layer of the wool. This is facilitated by the solvents which xe2x80x9cpushxe2x80x9d the active into the layer while at the same time providing the physical spreading described above.
Physical Stability
Because of the insolubility of the IGR in water, it is necessary to xe2x80x9csuspendxe2x80x9d the active in the formulation so that it does not settle on standing. If such settling occurs to a significant degree, then it is difficult to redisperse it to achieve an accurate dose rate for application to the animal. Thus, there is in effect a caking of the active at the bottom of the container. This is a major reason why many aqueous suspensions have problems. The result is that an animal treated with product from the upper part of the container is underdosed, while an animal treated with the product from the lower part of the container is overdosed. This may have fatal consequences.
Aqueous formulations of water insoluble IGRs are more accurately described as suspensions. It would be expected that when such formulations are applied to animals as pour-ons, the suspended active would remain at the site of application, thereby exacerbating the spreading problems described above. Furthermore, it has been shown that when other water insoluble actives are applied to animals such as sheep in an aqueous pour-on formulation, the majority of the active grows out with the wool staple, effectively being carried away from the skin surface where it is needed to control the parasites.
It has now been surprisingly found that an aqueous based pour-on formulation containing a water insoluble insect growth regulator(IGR) and a blend of surfactant and wetting agents is efficacious in controlling sheep lice. The formulation has the advantage over traditional non-aqueous solvent based formulations because it is rainfast and leads to very low pesticide tissue residue levels in the animals after application.
A surprising demonstration of the efficacy of this pour-on formulation is that at concentrations of 12.5 and 25.0 g/L diflubenzuron, when applied as a 20 ml dose along the backline of sheep, 100% lice kills were reported within 20 weeks. The majority of lice (95%) were killed within 10 weeks of application with the rest being killed over the remainder of the 20 week period.
It has also surprisingly been found that adding the formulations of this invention to an already wet animal does not affect the efficacy of the formulation. Likewise, if it rains shortly after the formulations of this invention are applied, the speed of efficiency of the active is increased compared to situations where no rainfall occurs after treatment. In both instances, it is believed that the surfactants promote the spread of the active over the surface of the animal.
Thus, in a first aspect, the present invention provides a topically acceptable aqueous pour-on formulation adapted for localised external application to an animal, which formulation includes an effective amount of a water insoluble insect growth regulator (IGR), a suspending agent, a surfactant or mixture of surfactants, and an aqueous carrier.
Because of the insolubility of IGR in water, it is necessary to suspend the active in the formulation so it does not settle on standing. Accordingly, it is necessary to include in the formulation a sufficient amount of a suspending agent.
In a second aspect, the present invention provides a method for controlling external parasites on an animal which method includes externally applying to an animal an effective amount of a aqueous pour-on formulation adapted for localised external application to an animal, which formulation includes an effective amount of a water insoluble IGR, a suspending agent, a surfactant or mixture of surfactants, and an aqueous carrier.
Any water insoluble IGR could be used in the formulation according to the present invention. Suitable IGRs include diflubenzuron, triflumuron, fluazuron, and methoprene. A particularly preferred IGR is diflubenzuron. For the formulation to be effective, the IGR must be suspended in the aqueous carrier.
Suitable suspending agents include xanthan gum, colloidal silica, bentonite, polyvinyl pyrrolidone, cellulose derivatives and alginates. The particularly preferred suspending agent is xanthan gum.
Any anionic or nonionic surfactant could be used in this formulation. A preferred anionic surfactant is alkylated naphthalene sulphonate, formaldehyde polymer, sodium salt. An effective amount of surfactant must be incorporated into the formulation to provide sufficient dispersant activity when applied to the animal. Preferred non-ionic surfactants are alkyl polysaccharides; alkyl phenol ethoxylates. A preferred alkyl phenol ethoxylate is nonyl phenol ethoxylate.
Other ingredients may be suitably included, for example, wetting agents, thickeners, humectants, preservatives, buffers, anti-foaming agents, diluents, excipients, adjuvants, and/or carriers. Actives which have an immediate effect (ie xe2x80x9cknock downxe2x80x9d); dyes (scourable, water soluble); antioxidants or UV stabilizers (eg oxybenzone); and thixatropic agents may also be added. A preferred humectant is polyethylene glycol.
Thus, in a third aspect, the present invention provides a method for formulating a topically acceptable aqueous pour-on formulation adapted for localised external application to an animal, which method comprises forming a first component by mixing a humectant and non-ionic surfactant until homogenous; adding water and mixing until homogenous; adding buffer and anionic surfactant; adding insect growth regulator (IGR); forming a second component by mixing humectant and thickener; and combining said first and second components.
Suitably, the first and second components are diluted to a desired and final volume.
In addition, suitably, the IGR is milled to form a particle size of between about 2 to about 5 xcexcm.
The xe2x80x9cnormalxe2x80x9d ratio of the above would be a) :b) :c) :d) :e)=5:6:1:1:1. A more general description of the ratio would be active:surfactants/wetting agents/thickeners=1:2. These ratios would not be expected to vary significantly with type of active or surfactants. The most effective ratio is that of the most preferred formulation which has been xe2x80x9cbalancedxe2x80x9d to optimise all of the above. The optimum pH for this formulation is in the range pH 5-9.
A particularly preferred formulation using the ranges of concentrations above would include diflubenzuron as the active; nonyl phenol ethoxylate, alkylated naphthalene sulfonate, formaldehyde polymer, sodium salt, as the mixture of surfactants; sodium lauryl sulfate as a wetting agent and Xanthan gum as a thickener or suspending agent.
Suitably, pour-on formulations include a colouring agent to enable the user to visually monitor the application of the formulation to the animal. The nature of the coloring agent is unimportant and a wide variety of suitable dyes and pigments will be known to the skilled person.
Suitably, the ingredients are formulated as follows: (a) half of the propylene glycol and non-ionic surfactant mixed in a mixing vessel until homogeneous. Water is then added and mixed until homogeneous. This is followed by buffer and anionic surfactant. Typically, anti-foam is then added and the mixture stirred. (b) The active ingredient is then added and mixed until homogeneous. (c) The second half of the propylene glycol is mixed with the Xanthan gum and then added and again, the mixture stirred well until thorough mixing has occurred. The final volume is then adjusted with water if necessary.
The pour-on formulation may be formulated for application by a spray technique, for example, as an aerosol using a liquid or gas as propellent.
Depending on the efficacy of the particular active agent used, the formulation will generally contain from about 5 to about 50 g/L of the active agent.
The external parasites which may be treated in accordance with this invention include ticks, fleas, flies (for example, sheep blow fly, buffalo fly, nuisance fly), lice (for example, cattle and sheep lice) and mites (for example, sheep mites). The insects and parasites mentioned are indicative only, and numerous other insects and parasites can be treated by the method of the present invention. Suitably, the compositions and method of this invention may be used to treat the sheep body louse which is classified as follows: Orderxe2x80x94Phthiraptera, Sub Orderxe2x80x94Mallophaga, Familyxe2x80x94Trichodectidae, Genusxe2x80x94Damalinia (Bovicola, Tricholdectes), Speciesxe2x80x94Bovicola ovis (Schrank).
The animal is preferably a mammal, and may be selected from sheep, cattle, deer, goats, pigs, dogs, and cats. The animal may also be a bird.